A number of different power conversion systems convert power from one form to another. For example, a multilevel power inverter is a power electronic device structured to produce alternating current (AC) waveforms from a direct current (DC) input voltage. These power conversion systems are used in a wide variety of applications, such as variable speed motor drives.
Isolation, and independent control within power conversion systems, is provided by gate drive circuitry. Gate drive circuits convert logic level control signals into appropriate voltages for switching one or more power devices within a power semiconductor group. In most cases, these circuits provide voltage isolation to prevent exposure of the logic signals to potentially dangerous high voltages on the power circuit.
Many conventional techniques provide isolation and control functionality via gate drive circuits. For example, one technique transfers a voltage directly across a barrier, via a transformer, while maintaining galvanic isolation. When using a transformer, a voltage common to terminals of the secondary is produced when a voltage step occurs within the power semiconductor group. This common voltage causes parasitic currents to flow through the control circuit, which can cause failure or unintended operation. Another technique uses fiber optic transmission for creating the digital on-off signal, while transferring power separately with an isolated power source. These conventional techniques, however, are costly and lack precision synchronization for controlling series connected power semiconductor devices (e.g., switches).